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kevin gilmore

current feedback electrostatic amp

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On 7/10/2018 at 10:45 PM, mwl168 said:

This is a great sounding amp. For the parts cost (when you can get them), this ES CFA probably takes the crown of the ROI of all the ES amps I have built.

So Glad you like it. never sure what someone else will think / hear

its a  good thing I did not build this first

might have found an even more expensive hobby

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Bought these PCBs from the GB awhile back. Looking to order the in-stock resistors to start. Are the values shown currently good to use? The schematic done earlier is a little different. Thanks.

C323F877-913E-4768-BF4F-9156A2B0A23B.jpeg

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I compared the resistors to my board and, without seeing the trace, they look right.

This amp runs much hotter than I expected so make sure you have ample heatsink. The 500K bias resistors set the output current.   

Edited by mwl168

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FYI,

PBHV9560, PBHV8560, KSA1156 are all in-stock at Mouser and shipping.

KSA2752 are still BO until November.

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58 minutes ago, Laowei said:

FYI,

PBHV9560, PBHV8560, KSA1156 are all in-stock at Mouser and shipping.

KSA2752 are still BO until November.

Kevin has noted that KSC5026 is a substitute for KSC2752. Last I checked it was BO at Mouser but in stock at Digikey!

Edited by mwl168

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On 8/18/2018 at 4:24 PM, Laowei said:

the values shown 

Yes, have made boards from those gerber's and they work just fine.

51 minutes ago, Laowei said:

KSA2752 are still BO until November.

when I last ordered some (19-Oct-2017) it said Jan 2018

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54 minutes ago, mwl168 said:

Kevin has noted that KSC5026 is a substitute for KSC2752. Last I checked it was BO at Mouser but in stock at Digikey!

Thanks. I’ll give Digikey my order. Looks like I’ll have all the parts to try the little amp out. I’ll repurpose the PS from my KGST to power it.

56 minutes ago, congo5 said:

Yes, have made boards from those gerber's and they work just fine.

when I last ordered some (19-Oct-2017) it said Jan 2018

Thanks for the resistor confirmation. The BO slide on that BJT is not too encouraging... 

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The transistors on the inside, Don´t need a heatsink?

For the temperatures that Mwl says, I think I'll need a big chasis.

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9 hours ago, jose said:

The transistors on the inside, Don´t need a heatsink?

No

9 hours ago, jose said:

For the temperatures that Mwl says, I think I'll need a big chasis.

 0,5 C°/W per channel will do if you go with stock values

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For resistors I used Koa like in other electrostatic amps. Transistors is OK. Front transistors I used PBHV8560/PBHV9560

 

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1 hour ago, jose said:

For resistors I used Koa like in other electrostatic amps. Transistors is OK. Front transistors I used PBHV8560/PBHV9560

 

Thanks...  Is metal film 1/4 watt 1% 100 ppm ok?  Is one series better than another

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12 minutes ago, sbelyo said:

Thanks...  Is metal film 1/4 watt 1% 100 ppm ok?  Is one series better than another

Nop, for electrostatic amps I use this KOA. Metal film 1/2W 1% 50 ppm (or 100 ppm) 

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2 minutes ago, jose said:

Nop, for electrostatic amps I use this KOA. Metal film 1/2W 1% 50 ppm (or 100 ppm) 

cool thanks

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I thought it was either the Xicon 271 or 273 series resistors that we’re used for the electrostatic amps? I could be wrong/behind the times...


Sent from my iPhone using Tapatalk

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32 minutes ago, Pars said:

I thought it was either the Xicon 271 or 273 series resistors that we’re used for the electrostatic amps? I could be wrong/behind the times...


Sent from my iPhone using Tapatalk

The problem with Xicon is max volt: 

350v max (271 series), 500v max (294 series) vs 700v max (Koa MF1 series 1/2w).

Edit: I'm reviewing the technical sheets and I see that the data is similar for both the Xicon (293 series) and the KOA (CF1). All my BOMs are with KOA resistors 

 

Edited by jose
add dates

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I just realized that the terminal blocks should be high voltage as well.

Jose, what terminal block are you using?

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Koa 1/2W (MF series IIRC) and RD60 should be fine in most positions with Electrostatic amps. I’ve used both without issues.

From what I read, the Xicon is better for the battery positions in Kevin’s T2 - others seem to result in noise issues likely due to leakage.

Edited by mwl168

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 I haven´t predilection for any particular resistors brand. I use what works but if there are better ones for these amplifiers, I'll buy them of course.

For terminal I think we all use the same Phoenix (MKDSN series).

 

 

 

 

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18 hours ago, jose said:

For terminal I think we all use the same Phoenix (MKDSN series).

I measured the pin spacing on the boards as well as the BH Ultramini PSU.  They're all 5.08mm  The MKDSN series are all 7.62mm

It doesn't look like they'll fit and I don't see anything in that size higher than 300V

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